As well known, the name long term evolution (LTE) is so-named in the meaning of technology which enhanced the third generation mobile communication in the long term; at the present time it is considered as one of the strong candidates including WiBro Evolution for the fourth generation mobile communication technology.
The LTE is based on the standard ‘Release 8’ finalized in December 2008 by the 3rd Generation Partnership Project (3GPP) which is a standards organization for 3rd generation mobile wireless communication; the channel bandwidths are from 1.25 to 20 MHz, the maximum transmission speed of a downlink is 100 Mbps for 20 MHz bandwidth, and the maximum transmission speed of an uplink is 50 MHz.
Wireless multiple access and duplexing methods are based on orthogonal frequency division multiplexing (OFDM), and high speed packet data transmission method is based on multiple-input and multiple-output (MIMO). LTE Advanced is an evolved version of an LTE, hereinafter all of these will be referred to as a ‘3GPP LTE.’
Meanwhile, two types of techniques are provided for separating an uplink from a downlink in an LTE system. The first one is frequency division duplexing (FDD) technique which separates an uplink from a downlink with frequency bands, The second one is time division duplexing (TDD) technique which separates an uplink from a downlink with a time domain.
FIG. 1 is a table defining the lengths of transmission intervals of an uplink and a downlink in a frame structure of a TDD based LTE system. The lengths of transmission intervals of the uplink and the down link in time domain for TDD based LTE system are determined by the signal called ‘UL/DL configuration’ as illustrated in FIG. 1, according to the values thereof the uplink and the down link are classified into total of 7 types. In FIG. 1, “D” represents a downlink sub-frame, “U” represents an uplink sub-frame, “S” represents a special sub-frame where both downlink data and uplink data are transmitted simultaneously; length of one frame is 10 ms and length of each sub-frame is 1 ms, so there are total 10 sub-frames in a frame. In FIG. 1, for example, in configuration 1, switching from downlink to uplink occurs with 5 ms period, thus in each frame there are 4 downlink sub-frames, 4 uplink sub-frames, and 2 special sub-frames respectively.
FIG. 2 is a typical block diagram of a signal analyzer for an LTE system. As illustrated in FIG. 2, a typical signal analyzer for an LTE system, that is LTE test equipment, is provided with a layer 3 processing unit 100, a layer 2 processing unit 200, and a layer 1 processing unit 300. The layer 3 processing unit 100 is responsible for the processing of Internet Protocal (IP).
Layer 2 processing unit 200 comprises: a packet data convergence protocol (PDCP) which performs IP header compression and decompression, user data transmission, and maintenance of sequence number for radio bearers, and the like; a radio link control (RLC) which is responsible for the processing of hybrid automatic repeat request (HARQ) related to transmission error control; and a media access control (MAC) processing unit which is a sub-layer of data transmission protocol and a part of the data link layer. Finally, layer 1 processing unit 300 is responsible for the processing of physical layer (PHY).
Meanwhile, in a signal analyzer for an LTE system of the prior art, a layer 3 processing unit 100 is usually implemented in a general purpose operating system such as Windows or Linux which is being processed by the CPU; a layer processing unit 200 is implemented with an exclusive firmware which is being processed by the digital signal processor (DSP); and a layer 1 processing unit 300 is implemented with a firmware processed by the DSP or the field programmable gate array (FPGA). However, while the layer 2 processing unit 200 and the layer 1 processing unit 300 can sufficiently handle an event for 1 ms which is corresponding to one sub-frame, the layer 3 processing unit 100 cannot handle an event for 1 ms since it is implemented in a non-real time OS such as Windows or Linux. For this reason, in the layer 2 processing unit 200, the IP data received from the layer 3 processing unit 100 is being buffered and processed every 1 ms for transmitting to the layer 1 processing unit 300. However, according to a TDD downlink data processing technique as described above, the transport block size of the downlink data in the special sub-frame is only maximum 75% of the transport block size of a regular downlink sub-frame, in other words, since there is a difference in the transport block size of the downlink data between the special sub-frame and the downlink sub-frame, data loss problem occurs when the buffered data is transmitted every 1 ms.
To solve this problem, a method is adopted in the prior art, wherein data is being transmitted without allocating downlink data to the special sub-frame (method A), or data is being transmitted after reducing the transport block size of all the downlink sub-frames to the transport block size of the special sub-frame (method B).
However, in case when the above described method A and method B are adopted, there is an efficiency degradation problem owing to lower throughput rate for each UL/DL configuration as shown in the right side of FIG. 1 when compared with a case where data is being transmitted with maximum transport block size of the downlink sub-frame and the special sub-frame